Although several investigators have suggested that possibly a neural system exists that is capable of inhibiting ACTH secretion, no such system has ever been identified. This project is designed to investigate if a neural inhibitory system is involved in the regulation of ACTH release and, if such a system does exist, to identify the components of the inhibitory system. These studies will specifically concentrate on the role of the limbic system and midbrain in modulating the hypothalamic regulation of ACTH release in relation to (a) circadian fluctuations of resting levels, (b) surgical stress, (c) emotional stress, and (d) ontogeny of the neural modulation of ACTH release.